1. Field of the Invention
The present invention relates to a vehicle travel control apparatus, and more particularly, to a vehicle travel control apparatus including a plurality of travel motion state control devices for operating so as to cause a travel motion state of a vehicle to approach a target travel motion state.
2. Description of the Related Art
When the vehicle receives an external force during travel, the travel motion state of the vehicle deviates from a target travel motion state. For example, when the vehicle receives a crosswind during the travel, a leeward lateral force acts on the vehicle, and a yaw moment deflecting a travel direction of the vehicle leeward is generated by the action of the lateral force, and an unnecessary yaw rate is thus generated on the vehicle.
There have been known various travel motion state control devices for operating so as to cause the vehicle travel motion state to approach the target travel motion state, thereby preventing the travel motion state of the vehicle from deviating from the target travel motion state. Those travel motion state control devices provide a braking/driving force difference between left and right wheels, or increase slip angles of the wheels to increase cornering forces of the wheels, to thereby generate a control yaw moment against the yaw moment caused by the external force acting on the vehicle. Moreover, there has also been known a travel motion state control device for using an aerodynamic force to generate the control yaw moment.
For example, in Japanese Patent No. 3463375, there is disclosed a control device for using control of distributing a driving force between the left and right wheels and an aerodynamic device such as side air spoilers, thereby generating and controlling the control yaw moment against the yaw moment caused by the crosswind.
An energy is required to operate the travel motion state control devices. In addition, a travel resistance of the vehicle is increased, for example, due to an increase in rolling resistances of the wheels or an air resistance of the vehicle, which results from the operations of the travel motion state control devices. A loss of energy is generated by those factors. Even a device highest in an effect of controlling the travel motion state may have a large loss in the energy, and the control effect and the loss in the energy change depending on the travel state of the vehicle and the state of the external force.
However, the related-art vehicle travel control apparatus including the plurality of travel motion state control devices capable of generating the control yaw moment controls the travel motion state by using a device or combination of devices highest in the control effect. As a result, even if the travel motion state of the vehicle can be effectively controlled, energy efficiency of the control of the travel motion state may deteriorate, resulting in deterioration of fuel efficiency of the entire vehicle.